: I'll be patching in the electrical connections into the electrical panel under the rear seat.

: Ground is obvious as is positive. But where can I connect to a line that is live only when the ignition is on?

: Any possibilities for connecting the auto-mute line to the radio?

You should have the existing BMW phone wiring in the truck. You can get ignition switched power there. Depending on the type of phone that it is you might now have the right interface for the audio mute.

I have a motorola car kit for the flip phone and eneded up not poking around as I didn't want to fry the phone or the car.